Supplied air helmets are regularly worn in environments where the surrounding air contains contaminants. These helmets have a fluid impermeable visor that is located in front of the wearer's face when the helmet is worn. The visor has a window that allows the wearer to see the surrounding environment. A face seal is attached to the visor to separate a breathing zone or an interior gas space from the surrounding exterior gas space. The interior gas space is located between the visor and the wearer's face and is defined, for the most part, by the face seal that is attached to the visor, the visor body, and the wearer's face. U.S. Pat. Nos. 6,014,971, 4,462,399, and 4,280,491 disclose examples of supplied air helmets that use face seals for this purpose.
Clean air is forced into the interior gas space from a supply tank or from a powered air source that drives ambient air through an air filter. The wearer breathes this clean air and exhales it back into the breathing zone. This exhaled air, along with excess clean air that is forced into the breathing zone, exits the interior gas space through openings in the face seal. The positive pressure that generally occurs within the interior gas space precludes contaminants from entering the interior gas space through the openings. Welders, for example, often use supplied air helmets as protection from breathing contaminants generated during welding procedures. Examples of welding helmets are shown in the following patent documents: U.S. Pat. Nos. 6,557,174, 6,591,424, 6,185,739, 5,533,206, 5,191,468, 5,140,707, 4,875,235, 4,853,973, 4,774,723, 4,011,594 and Des. 398,421; and WO 00/59421 and WO 99/26502.
A variety of face seal constructions have been designed for providing a separation barrier between the interior gas space and the exterior gas space and for enabling the excess air within the interior gas space to be purged to the exterior gas space. U.S. Pat. No. 4,136,688, for example, describes using a row of bristles as a face seal material. In U.S. Pat. Nos. 5,533,500 and 5,104,432, check valves are mounted on a soft face seal pad to exhaust air from the mask interior. Some supplied air helmets have used Tyvek™ or Sontara™ from DuPont as the face seal material—see U.S. Pat. No. 6,250,299 B1 to Danisch et al. and U.S. Pat. No. 6,016,805 to Burns et al., respectively. Others have used a foam material—see U.S. Pat. No. 5,054,479. Some commercially available products have used a PVC coated fabric as the face seal. These products also have incorporated an elastic material around the edge of the face seal to enable it to conform to different shaped faces. Other commercially available products, such as the Performa A-VL face shield (available from North Safety Products of Middelburg, Netherlands), have used a woven fabric for the face seal. The woven fabric has had a ruffled free edge that extends radially inward from the visor to contact the wearer's face.
While known face seal products have provided a variety of constructions for establishing a boundary between the interior gas space and the surrounding environment, these known products have not been fashioned to enable air to be purged from the mask interior in a differentiated manner. The known products thus may not have fully optimized air flow within the supplied air helmet to improve comfort and to preclude air inflow from the surrounding environment.